1. Field of the Invention
The application relates to a method utilized in a wireless communication system, and more particularly, to a method of handling communication operations.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
The CA is introduced to the LTE-A system by which more than one cells can be aggregated to achieve a wide-band transmission. The CA increases bandwidth flexibility by aggregating the cells. When a UE is configured with the CA, the UE has the ability to receive and/or transmit packets via one or multiple cells to increase throughput.
Different from the LTE/LTE-A system operating in a frequency-division duplexing (FDD) mode (or simply FDD system), directions of subframes of a frequency band in the LTE/LTE-A system operating in a time-division duplexing (TDD) mode (or simply TDD system) may be different. That is, the subframes in the same frequency band are divided into UL subframes, downlink (DL) subframes and special subframes according to the UL/DL configuration specified in the 3GPP standard.
FIG. 1 is a table 10 of the UL/DL configuration with subframes and corresponding directions. In FIG. 1, 7 UL/DL configurations are shown, wherein each of the UL/DL configurations indicates a set of directions (i.e., transmission directions) for 10 subframes, respectively. Each subframe is indicated with respective subframe number (i.e., subframe index) in FIG. 1. In detail, “U” means that the subframe is a UL subframe where UL data is transmitted, and “D” means that the subframe is a DL subframe where DL data is transmitted. “S” means that the subframe is a special subframe where control information and maybe data (according to the special subframe configuration) is transmitted, and the special subframe can also be seen as the DL subframe in the present invention. Note that the eNB may configure a UL/DL configuration to a UE via a higher layer signaling (e.g., System Information Block Type 1 (SIB1)) or a physical layer signaling (e.g., DL control information (DCI)).
As stated previously, a UE may perform a communication operation via multiple cells, when the UE is configured with the CA, wherein the communication operation may be a transmission (from the UE to the network) or a reception (from the network to the UE), e.g., of a packet or a message. However, it may happen that UL/DL configurations of the cells are different, e.g., when an inter-band CA is configured to the UE. It may also happen that the cells jointly operate in different modes, e.g., in time-division duplexing (TDD) mode and/or frequency-division duplexing (FDD) mode. In the above situations, directions of a subframe (e.g., which are determined according to the UL/DL configurations of the cells) may be different, and it is difficult for the UE to decide how to perform the communication operation in the subframe. The problem is especially severe for a half-duplex UE which can only perform one of the transmission and the reception at the same time (e.g., in the same subframe). In another example, the UE may fail to transmit or receive a hybrid automatic repeat request (HARQ) feedback when one or more communication operations cannot be performed, i.e., HARQ discontinuity.
Thus, the conflict caused by different UL/DL configurations of the cells is an important problem to be solved.